The present invention relates to a pump light source for an optical fiber amplifier in a wavelength multiplexing optical communication system; and, more particularly, to a dual wavelength optical fiber laser which forming two independent resonators through two groups of short period gratings and a wavelength division multiplexing (hereinafter, referred to as a WDM) coupler, and removing an interference between the two resonators by using a long period grating.
Recently, researches in an ultra wide band light amplifying technology over 1.4 xcexcmxcx9c1.6 xcexcm wavelength band by utilizing low loss wavelength band in an optical fiber for obtaining an optical communication speed about dozens of terabit is in progress. An optical fiber Raman amplifier, which is expected to contribute to a long-distant optical communication development, determines an amplifying wavelength band by a pump light so, in case of using a dual wavelength pump light, it can broad the amplifying band easily.
In a conventional method, the dual wavelength pump light source is realized by combining two different output wavelengths of laser diodes or optical fiber lasers.
Generally, the laser diode or the optical fiber laser generates a light in a single wavelength so wavelengths in two independent light sources have to be coupled to form the dual wavelength laser by using a wavelength-multiplexing device.
Hereinafter, a conventional dual wavelength laser operation obtaining method will be described in detail referring to the accompanying drawings.
Normally, the dual wavelength pump light source is realized by combining two different output wavelengths of laser diodes or optical fiber lasers through the wavelength-multiplexing device.
As referred in FIG. 1, in a conventional method, the different two wavelengths realize the dual wavelength laser by using a mach-zehnder field filter.
In FIG. 1, an optical waveguide 11, which has the mach-zehnder form, is used to combine the different two wavelengths xcex1 and xcex2. In this case, the optical waveguide 11 uses an interference phenomenon so, an incident light, which has a narrow band and a stable wavelength, is required. To achieve the incident light, the two wavelengths xcex1 and xcex2 are stabilized through gratings 12, 13 and then injected to the mach-zehnder optical waveguide 11.
However, an insertion loss is generated for inputting the light into the optical waveguide 11, and when a wavelength changes are happened, a coupling loss in the pump light source is produced due to the interference characteristics of the mach-zehnder filters. Additionally, comparing to the optical fiber, the optical waveguide 11 may be easily damaged when a high power laser is incidented.
FIG. 2 is a diagram showing conventional dual wavelength laser structure using a WDM coupler. Another words, the WDM coupler 21 which is manufactured in an optical fiber fusion method is used for coupling the two different wavelengths xcex1 and xcex2, and in this case, a high power operation is possible. However, a WDM coupler for a narrow wavelength band, e.g., a narrow wavelength band smaller than 40 nm is hard to manufacture and shows high loss and polarization dependency, so it is difficult to couple near located two wavelengths.
Also, the methods in FIGS. 1 to 2 need independent two pump sources to realize the dual wavelength laser, so a production cost is increased.
It is, therefore, an object of the present invention to provide a dual wavelength laser structure which needs no additional pump light source for operating the dual wavelength laser and is not using a mach-zehnder optical waveguide coupler so that an inpsertion loss and a coupling loss in the pump light is solved. Also, an object of the present invention is to provide the dual wavelength laser structure of having relatively simple structure, which is economical and has good high power operation characteristics and two adjacent wavelengths operation is possible.
In accordance with one aspect of the present invention, there is provided a dual wavelength optical fiber laser, comprising: a first and a second optical fibers which generating stimulated scattering by a pump light source; two short period optical fiber gratings that is resonating each of a first and a second wavelength light which are generated by the optical fibers and regulating reflecting characteristics according to the first and the second wavelengths; a WDM optical fiber coupler which inputs a pump wavelength to the optical fibers and outputs a laser operation wavelength; and an interference removing means which is connected between the optical fibers and removes an interference in the first and the second wavelength of resonating.
In accordance with another aspect of the present invention, there is provided a dual wavelength optical fiber laser, comprising: a first and a second optical fibers which generating stimulated scattering by a pump light source; a WDM optical fiber coupler which inputs a pump wavelength to the optical fibers and outputs a laser operation wavelength; a first resonating means which is formed with the first optical fiber and a first group of a short period optical fiber grating, and thereby resonating a first wavelength light which is generated from the first optical fiber; a second resonating means which is formed with the second optical fiber and a second group of a short period optical fiber grating, and thereby resonating a second wavelength light which is generated from the second optical fiber; an interference removing means for removing an interference between the two resonating means by locating between the first and the second resonating means; and a pump light reflecting means which is connected to a laser outputting edge of the WDM optical fiber coupler to reflect a pump wavelength of the pump light source, then re-injected to the first and the second optical fibers.
Preferably, the interference removing means uses a long period optical fiber grating which has high loss to the first wavelength and the second wavelength, simultaneously, and additionally uses long period optical fiber gratings which show high loss to the first wavelength and to the second wavelength, respectively.
Preferably, the first group of the short period optical fiber grating is directly carved to a couple region of the WDM optical fiber coupler.